Rotaviruses are the single most important agent of acute gastroenteritis, a disease which requires hospitalization of infants and young children in developed countries, and a frequent cause of death in children less than 5 years of age in developing regions of the world. Studies in the United States, Australia, and Japan have demonstrated that between 34 and 63% of hospitalizations of children for acute diarrheal disease are associated with rotavirus infection [A. Z. Kapikian et al, Rev. Infect. Dis., 2:459-469 (1980)]. The incidence of hospitalization for rotavirus gastroenteritis in a health maintenance organization in the U.S. was estimated to be 222 per 100,000 in children from 13 to 24 months of age, and 362 per 100,000 in those less than one year [W. Rodriguez et al, Am. J. Dis. Child., 13:777-779 (1980)]. Infection with rotavirus was associated with 63% of all hospitalizations for acute diarrhea in this pediatric population [W. Rodriguez et al, cited above]. A recent review of mortality data in the U.S. from 1973 to 1983 indicated that 500 deaths per year occur in children less than 4 years old due to diarrheal diseases, and that 20 to 80% of excess winter deaths due to diarrhea in the U.S. are associated with rotavirus infections [M -S. Ho et al; JAMA, 26:3281-3285 (1988)]. Rotaviruses are also responsible for a substantial proportion of the mortality associated with diarrheal diseases in third world countries. An effective rotavirus vaccine would therefore have a major impact on the health of children in both the developed and developing areas of the world.
Rotaviruses have an inner and outer capsid with a double-stranded RNA genome formed by eleven gene segments. Multiple serotypes have been defined by plaque reduction neutralization tests, and studies of reassortant viruses have demonstrated that two outer capsid proteins, v.p.7 and v.p.4, are the determinants of virus serotype. The v.p.7 protein is coded for by either gene segment 7, gene segment 8 or gene segment 9 of the particular human rotavirus. The location of the v.p.7 encoding gene may be determined for each specific rotavirus by conventional experimental methods. The protein v.p.4 is an 88,000 dalton major surface structural protein product of gene 4 of a rotavirus. Like v.p.7, it functions as a major serotype-specific antigen, operative in serum neutralization (SN) tests, capable of inducing serotype-specific neutralizing antibody, and capable in a mouse system of inducing serotype specific immune protection against rotavirus disease. [See, Offit et al, (1986) supra]. In some earlier references, the v.p.4 was referred to as v.p.3. After 1988, a change in nomenclature, resulted in the more proper reference to this protein as v.p.4 [M. Liu et al, Virol., 16:26-32 (1988) and M. K. Estes et al, Immunol. Invest., 18:571-581 (1989)].
Since the gene segments encoding the v.p.7 and v.p.4 proteins segregate independently [Y. Hoshino et al, Proc. Natl. Acad. Sci. USA, 12:8701-8704 (1985) and P. Offit et al, J. Virol., 57:376-378 (1986)], it has been proposed that serotyping nomenclature include both the G type, determined by v.p.7, and the P type, determined by v.p.4 [M. Estes et al, Microbiological Reviews, 52:410-449 (1989)]. Most human rotavirus infections in the U.S. are caused by viruses of G types 1, 2, 3, or 4, and P types 1, 2, or 3 [V. Gouvea et al, J. Infect. Dis., 162:362-367 (1990), P. Woods et al, J. Clin. Microbiol., 30:781-785 (1992), and J. Gentsch et al, J. Clin. Microbiol., 30:1365-1373 (1992)]. However, other human rotavirus types, including for example, type G9, are more prevalent in Asia, Europe and certain third world countries.
A number of animal rotaviruses are attenuated in humans, and have been evaluated as potential live rotavirus vaccines, including the bovine serotype G6 WC3 rotavirus. The WC3 vaccine virus was shown to be immunogenic and non-reactinogenic in infants [H F. Clark et al, American Journal Diseases of Children, 140:350-356 (1986) and H F. Clark et al, J. Infect. Dis., 158:570-587 (1988)], but was inconsistent in providing protective immunity against human rotavirus infection [H F. Clark et al, J. Infect. Dis., 15:570-587 (1988), D. Bernstein et al, J. Infect. Dis., 162:1055-1062 (1990), and M. Georges-Courbot et al, Res. Virol., 142:405-411 (1991)]. However, it has been proposed that serotype-specific immunity is necessary to induce consistent protection against rotavirus diarrhea [J. Flores et al, Lancet, 1:882-884 (1987) and C. Christy et al, Pediatr. Infect. Dis., 7:645-650 (1988)].
There exists a need in the art for effective vaccines providing protective immunity against rotavirus infection and the severe clinical symptoms associated therewith.